NOTE: Before changing out a battery in a nGWY2 CTRL, please make sure the unit has been powered down for a few minutes.
Battery Type - BR1225 (NOTE: In the video linked below it shows in a popup still frame a CR2025 battery. The 2025 battery will not fit as it is 7.5mm larger in diameter. The BR1225 is the correct battery. See the image pasted immediately below for correct part number(s) for the nGWY2 battery as it varies by mfr)
If the nGWY2 CTRL does not hold its date/time upon loss of power, the battery in the unit should be replaced. Please note, all programming, schedules, profiles, etc. are stored within non-volatile memory on the Gateway. None of this programming will be lost if the Gateway has a dead battery.
There is a video available at the following link that demonstrates how to replace this battery: Video On Replacing Gateway V2 Battery